1. Field of the Invention
The invention relates to a process and apparatus for in-situ rejuvenating solid catalyst particles suspended in a slurry. More particularly, the invention relates to a process and means for rejuvenating solid catalyst particles dispersed in a three phase, Fischer-Tropsch type hydrocarbon slurry comprising said particles, a hydrocarbon liquid phase and gas bubbles in-situ in the slurry, in which gas bubbles are removed from the slurry entering the rejuvenation zone.
2. Background of the Invention
Slurry hydrocarbon synthesis (HCS) processes are known. In a slurry HCS process a synthesis gas (syngas) comprising a mixture of H.sub.2 and CO is bubbled up as a third phase through a slurry in a reactor in which the slurry liquid comprises hydrocarbon products of the synthesis reaction and the dispersed, suspended solids comprise a suitable Fischer-Tropsch type hydrocarbon synthesis catalyst. Reactors which contain such a three phase slurry are sometimes referred to as "bubble columns", as is disclosed in U.S. Pat. No. 5,348,982. Irrespective of whether the slurry reactor is operated as a dispersed or slumped bed, the mixing conditions in the slurry will typically be somewhere between the two theoretical conditions of plug flow and back mixed. Syngas made from hydrocarbon feedstocks which contain nitrogen (i.e., natural gas) or nitrogen containing compounds (i.e., resids, coal, shale, coke, tar sands, etc.) invariably contains HCN and NH.sub.3 which contaminate the reactive slurry and rapidly, but reversibly, deactivate the catalyst. Certain oxygenates and carbonaceous compounds formed in the slurry as by-products of the HCS reaction can also cause rapid deactivation. Deactivation of such catalysts by these species is reversible and catalytic activity is restored (the catalyst rejuvenated) by contacting the deactivated catalyst with hydrogen. The activity of the HCS catalyst in the reactive slurry may be intermittently or continuously rejuvenated by contacting the slurry with hydrogen or a hydrogen containing gas to form a rejuvenated catalyst slurry as is disclosed, for example, in U.S. Pat. Nos. 5,260,239 and 5,268,344. In these patents the slurry, containing gas bubbles, is rejuvenated by circulating it through either a rejuvenation tube immersed in the slurry or in an external rejuvenation reactor. It has now been found that the presence of CO hinders catalyst rejuvenation until the CO is consumed. This limits the overall efficiency of the rejuvenation process and wastes CO and H.sub.2. It would be an improvement to the art if these gas bubbles could be removed from the slurry before it contacts the rejuvenation gas.